A push type driving belt to be used in a belt type continuously variable transmission is known in the prior art. The driving belt of this kind is formed by annularly juxtaposing a plurality of plate members called an “element” or a “block” in a same orientation, and by fastening the juxtaposing plate members by an annular member such as a band, a hoop and a ring.
One example of the above-explained driving belt is disclosed in Japanese Patent Laid-Open No. 2006-266363. According to the “transmission belt” taught by Japanese Patent Laid-Open No. 2006-266363, an element comprises a first hole and a first projection formed at a head part, and a second hole and a second projection formed in an inner circumferential side of a rocking edge. A plurality of the elements thus formed are fastened by a ring in a circular manner to form the transmission belt. According to the transmission belt taught by Japanese Patent Laid-Open No. 2006-266363, therefore, the first projection is inserted into the first hole but the second hole and projection are disengaged from each other in a straight region of the transmission belt between pulleys. Meanwhile, in a curved region of the transmission belt around the pulley, the first hole and the first projection are disengaged from each other but the second projection is inserted into the second hole.
Thus, the conventional driving belt is assembled by fastening the array of the element having the projection using the ring. However, in case of inserting a last piece of the element into the array of the elements, a sufficient clearance wider than the projection is required in the element array in order to avoid interference of the projection of the element to be inserted into the element array with the adjacent element already fastened by the ring. Therefore, as shown in FIG. 23, an endplay as a total of clearances among the elements remains inevitably in the element array of the assembled belt. However, in case the end play is too small, the last piece of the element is difficult to be inserted into the element array and easiness or productivity of the driving belt is thereby degraded. To the contrary, in case the end play is large, the last piece of the element is easy to be inserted into the element array. In this case, however, a transmission loss is increased due to a slippage between the elements and the ring, and a power transmitting efficiency is thereby degraded.
The last piece of the element can be inserted into the element array easily by shortening the projection even if the endplay is narrow. However, a fundamental role of the projection and the hole is to align the elements being juxtaposed. Therefore, if the length of the projection is too short, the element array cannot be aligned. In addition, durability and transmission efficiency of the driving belt may be degraded.
In order to solve the problems concerning the end play of the driving belt, Japanese Patent Laid-Open No. 2004-293634 discloses a “metal belt” using a plurality of spring means for contacting the elements in an element array by widening a clearance between the elements to which the spring means is inserted. According to the teachings of Japanese Patent Laid-Open No. 2004-293634, therefore, the elements can be kept in contact with each other in a region from an output pulley to an input pulley in a direction of movement. In addition, the elements can also be contacted to each other in a region toward a compression side where the belt is contacted with an input pulley to be rotated therewith. For this reason, clearances among the elements in the region to be contacted with the input pulley of the compression side are eliminated so that an occurrence of slippage of the element can be prevented in this region.
However, according to the teachings of Japanese Patent Laid-Open No. 2004-293634, the above-explained plurality of “spring means” are arranged in the metal belt. That is, in addition to the basic elements, a plurality of elements serving as “spring means” have to be assembled to form the metal belt. Therefore, an assembly cost and number of assembling steps of the metal belt have to be increased in comparison with those of the other conventional driving belts. In addition, when the metal belt is subjected to a load, the “spring means” in the compression side is compressed, and the “spring means” in a decompression side is decompressed to be elongated a direction to push the elements of both sides. Therefore, when those “spring means” are thus deformed, the “spring means” and elements slip inevitably on the ring. Thus, the transmission loss resulting from the slippage may not be reduced sufficiently even if the “spring means” are used in the driving belt.
Therefore, the conventional driving belt thus formed by fastening a plurality of elements annularly by a ring has to be improved to facilitate the assembling work thereof by ensuring the endplay appropriately, while reducing the endplay to improve the power transmitting efficiency thereof.